EP4546444A1 - Batterie secondaire et dispositif électrique - Google Patents

Batterie secondaire et dispositif électrique Download PDF

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Publication number
EP4546444A1
EP4546444A1 EP23921644.3A EP23921644A EP4546444A1 EP 4546444 A1 EP4546444 A1 EP 4546444A1 EP 23921644 A EP23921644 A EP 23921644A EP 4546444 A1 EP4546444 A1 EP 4546444A1
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Prior art keywords
based material
carbon
silicon
optionally
negative electrode
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EP23921644.3A
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German (de)
English (en)
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EP4546444A4 (fr
Inventor
Liangbin Liu
Jiazheng WANG
Chen Zeng
Meng KANG
Jingxian DENG
Zijian LV
Shuai XIE
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Contemporary Amperex Technology Hong Kong Ltd
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Contemporary Amperex Technology Hong Kong Ltd
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Publication of EP4546444A1 publication Critical patent/EP4546444A1/fr
Publication of EP4546444A4 publication Critical patent/EP4546444A4/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This application pertains to the field of battery technologies, and specifically, relates to a secondary battery and an electric apparatus.
  • secondary batteries have been widely used in energy storage power supply systems such as hydroelectric, thermal, wind, and solar power plants, and many other fields including electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • energy storage power supply systems such as hydroelectric, thermal, wind, and solar power plants
  • many other fields including electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • secondary batteries there are more demanding requirements for their performance, such as the need for secondary batteries to combine the energy density, rate performance, service life, and other performances.
  • This application provides a secondary battery and an electric apparatus, which can enable the secondary battery to have both good rate performance and cycling performance while having high energy density.
  • a first aspect of this application provides a secondary battery, including a negative electrode plate, where the negative electrode plate includes a negative electrode current collector and a negative electrode film layer, the negative electrode film layer has a first surface far away from the negative electrode current collector and a second surface arranged opposite the first surface, the negative electrode film layer has a thickness denoted as H, a region within a thickness range from the second surface of the negative electrode film layer to 0.3H is denoted as a first region of the negative electrode film layer, and a region within a thickness range from the first surface of the negative electrode film layer to 0.3H is denoted as a second region of the negative electrode film layer.
  • the first region includes a first active material
  • the second region includes a second active material
  • the first active material includes a first carbon-based material and a first silicon-based material, the first carbon-based material includes primary particles, and the first silicon-based material includes secondary particles formed by aggregating primary particles.
  • the first active material of the negative electrode film layer includes the first carbon-based material and the first silicon-based material, the first carbon-based material includes the primary particles, and the first silicon-based material includes the secondary particles formed by aggregating primary particles, so that the secondary battery can have both good rate performance and cycling performance while having high energy density.
  • the first carbon-based material has a carbon enveloping layer on its surface, and optionally the carbon enveloping layer includes hard carbon. This helps further optimize the rate performance of the secondary battery.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number is ⁇ 70%, and optionally 75% to 90%. This is beneficial for the secondary battery to have both good cycling performance and rate performance as well as relatively high energy density.
  • a proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number is ⁇ 55%, and optionally 60% to 85%. This is beneficial for the secondary battery to have both good cycling performance and rate performance as well as relatively high energy density.
  • a porosity of the first silicon-based material being the secondary particles is ⁇ 4%, and optionally 5% to 20%. Further adjusting the porosity of the first silicon-based material being the secondary particles helps further optimize the rate performance of the secondary battery.
  • a particle size by volume D v 50 of the first carbon-based material is 10 ⁇ m to 16 ⁇ m, and optionally 12 ⁇ m to 14 ⁇ m. With the particle size by volume D v 50 of the first carbon-based material falling within the foregoing range, it is favorable to improve the transport performance of ions and electrons, thereby further improving the rate performance of the secondary battery. In addition, it can also reduce the specific surface area of the first carbon-based material and reduce side reactions, thereby further improving the cycling performance of the secondary battery.
  • a particle size by volume D v 90 of the first carbon-based material is 20 ⁇ m to 28 ⁇ m, and optionally 22 ⁇ m to 26 ⁇ m. With the particle size by volume D v 90 of the first carbon-based material falling within the foregoing range, the first carbon-based material particles have good consistency, which is conducive to improving the transport performance of ions and electrons, thereby further improving the rate performance of the secondary battery.
  • the first carbon-based material meets (D v 90-D v 10)/D v 50 being 0.8 to 1.6, and optionally being 1.1 to 1.4.
  • (D v 90-D v 10)/D v 50 of the first carbon-based material falling within the foregoing range, the packing performance of the first carbon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the first carbon-based material is 1.0 m 2 /g to 1.8 m 2 /g, and optionally 1.2 m 2 /g to 1.6 m 2 /g. With the specific surface area ofthe first carbon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the first carbon-based material under 20000 N is 1.75 g/cm 3 to 2.0 g/cm 3 , and optionally 1.8 g/cm 3 to 1.95 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the first carbon-based material is 1.1 g/cm 3 to 1.3 g/cm 3 , and optionally 1.15 g/cm 3 to 1.25 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a degree of graphitization of the first carbon-based material is ⁇ 93%, and optionally 94% to 96%. With the degree of graphitization of the first carbon-based material falling within the foregoing range, it helps improve the ion transport performance of the negative electrode film layer, so that the secondary battery can have both high energy density and good rate performance.
  • a gram volume of the first carbon-based material is ⁇ 360 mAh/g, and optionally 361 mAh/g to 365 mAh/g.
  • the energy density of the secondary battery can be increased, and the carbon-based material can also be enabled to have good ion transport performance, which also helps improve the rate performance of the secondary battery.
  • a powder OI value of the first carbon-based material is 5 to 15, and optionally 7 to 12.
  • the first carbon-based material has a relatively small powder OI value, so can quickly receive ions from the positive electrode, thereby further improving the rate performance of the secondary battery.
  • the first carbon-based material includes graphite, and optionally the graphite includes artificial graphite.
  • a proportion of the first carbon-based material in the first active material by mass is ⁇ 50%, and optionally 60% to 98%.
  • a particle size by volume D v 50 of the first silicon-based material is 8 ⁇ m to 15 ⁇ m, and optionally 10 ⁇ m to 13 ⁇ m.
  • a particle size by volume D v 90 of the first silicon-based material is 15 ⁇ m to 25 ⁇ m, and optionally 16 ⁇ m to 24 ⁇ m.
  • the ion intercalation channels in the negative electrode film layer can be increased, which is also favorable for the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the rate performance of the secondary battery.
  • the first silicon-based material meets (D v 90-D v 10)/D v 50 being 0.7 to 1.5, and optionally being 0.9 to 1.3.
  • (D v 90-D v 10)/D v 50 of the first silicon-based material falling within the foregoing range, the first silicon-based material particles has relatively good packing performance, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the first silicon-based material is 0.7 m 2 /g to 2.0 m 2 /g, and optionally 0.8 m 2 /g to 1.6 m 2 /g.
  • the specific surface area of the first silicon-based material falling within the foregoing range, the ion intercalation channels of the negative electrode film layer can be increased, which is favorable for the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the rate performance of the secondary battery.
  • the specific surface area ofthe first silicon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the first silicon-based material under 50000 N is 1.0 g/cm 3 to 1.7 g/cm 3 , and optionally 1.2 g/cm 3 to 1.6 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the first silicon-based material is 1.0 g/cm 3 to 1.5 g/cm 3 , and optionally 1.1 g/cm 3 to 1.4 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a powder resistivity of the first silicon-based material under 4 MPa is ⁇ 15 ⁇ cm, and optionally 0.5 ⁇ cm to 12 ⁇ cm.
  • the first silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, and silicon alloy material, and optionally, the first silicon-based material includes secondary particles formed by aggregation of at least one of the following primary particles: silicon oxide material primary particles containing neither alkali metal nor alkaline earth metal, silicon oxide material primary particles containing either alkali metal or alkaline earth metal, silicon-carbon material primary particles, elemental silicon primary particles, and silicon alloy primary particles.
  • the second active material includes second carbon-based material.
  • the second carbon-based material includes secondary particles formed by aggregation of primary particles, and a proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number is ⁇ 60%, and optionally 70% to 85%. This is favorable for the secondary battery to better have both good rate performance and good cycling performance.
  • the first carbon-based material has a carbon enveloping layer on its surface
  • the second carbon-based material has a carbon enveloping layer on its surface
  • a percentage of the carbon enveloping layer of the second carbon-based material by mass is greater than a percentage of the carbon enveloping layer of the first carbon-based material by mass
  • the rate performance of the secondary battery can be further improved; and by making the percentage of the carbon enveloping layer of the second carbon-based material by mass greater than the percentage of the carbon enveloping layer of the first carbon-based material by mass, ions can quickly migrate to the surface layer of the second carbon-based material, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a particle size by volume D v 50 of the second carbon-based material is less than a particle size by volume D v 50 of the first carbon-based material.
  • the second region and the first region of the negative electrode film layer can have an ideal compacted density difference, so that the porosity in the thickness direction of the negative electrode film layer better matches the ion concentration distribution, which helps improve the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution and is favorable for ion transport, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a specific surface area of the second carbon-based material is less than a specific surface area of the first carbon-based material.
  • a powder compacted density of the second carbon-based material under 20000 N is less than a powder compacted density of the first carbon-based material under 20000 N.
  • the second region and the first region of the negative electrode film layer can have a good pore structure that better matches the concentration distribution of ions in the thickness direction of the negative electrode film layer, which improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution and facilitates ion transport, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a tap density of the second carbon-based material is less than a tap density of the first carbon-based material.
  • a degree of graphitization of the second carbon-based material is lower than a degree of graphitization of the first carbon-based material.
  • a gram volume of the second carbon-based material is less than a gram volume of the first carbon-based material.
  • a powder OI value of the second carbon-based material is less than a powder OI value of the first carbon-based material.
  • a particle size by volume D v 50 of the second carbon-based material is 9 ⁇ m to 15 ⁇ m, and optionally 11 ⁇ m to 13 ⁇ m.
  • a particle size by volume D v 90 of the second carbon-based material is 20 ⁇ m to 26 ⁇ m, and optionally 21 ⁇ m to 25 ⁇ m.
  • the second carbon-based material meets (D v 90-D v 10)/D v 50 being 0.8 to 1.6, and optionally being 1.0 to 1.4.
  • (Dv90-Dv10)/Dv50 of the second carbon-based material falling within the foregoing range, the packing performance of the second carbon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the second carbon-based material is 0.5 m 2 /g to 1.5 m 2 /g, and optionally 0.7 m 2 /g to 1.2 m 2 /g. With the specific surface area ofthe second carbon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby also enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the second carbon-based material under 20000 N is 1.6 g/cm 3 to 1.8 g/cm 3 , and optionally 1.65 g/cm 3 to 1.75 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the second carbon-based material is 0.9 g/cm 3 to 1.2 g/cm 3 , and optionally 1.0 g/cm 3 to 1.1 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a degree of graphitization of the second carbon-based material is ⁇ 92.5%, and optionally 93% to 94%. With the degree of graphitization of the second carbon-based material falling within the foregoing range, it helps improve the ion transport performance of the negative electrode film layer, so that the secondary battery can have both high energy density and good rate performance.
  • the second carbon-based material includes graphite, optionally includes artificial graphite.
  • a proportion of the second carbon-based material in the second active material by mass is ⁇ 85%, and optionally 90% to 97%. This helps improve the rate performance of the secondary battery.
  • the second active material includes a second silicon-based material, which can further increase the energy density of the secondary battery.
  • the second silicon-based material includes one or more of primary particles and secondary particles formed by aggregation of primary particles, and optionally includes primary particles.
  • the second silicon-based material includes primary particles, and a proportion of the second silicon-based material being the primary particles in the second silicon-based material by number is ⁇ 60%, and optionally 70% to 95%.
  • the second silicon-based material is mainly primary particles, it helps reduce the probability of particle breakage and increase the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery.
  • a proportion of the second silicon-based material in the second active material by mass is less than a proportion of the first silicon-based material in the first active material by mass.
  • a particle size by volume D v 50 of the second silicon-based material is less than a particle size by volume D v 50 of the first silicon-based material.
  • a specific surface area of the second silicon-based material is less than a specific surface area of the first silicon-based material.
  • the specific surface area of the second silicon-based material helps reduce side reactions, thereby facilitating the secondary battery to have better cycling performance.
  • a powder compacted density of the second silicon-based material under 50000 N is greater than a powder compacted density of the first silicon-based material under 50000 N.
  • a tap density of the second silicon-based material is greater than a tap density of the first silicon-based material.
  • a powder resistivity of the second silicon-based material under 4 MPa is less than a powder resistivity of the first silicon-based material under 4 MPa.
  • a particle size by volume D v 50 of the second silicon-based material is 4 ⁇ m to 12 ⁇ m, and optionally 5 ⁇ m to 11 ⁇ m.
  • a particle size by volume D v 90 of the second silicon-based material is 8 ⁇ m to 18 ⁇ m, and optionally 9 ⁇ m to 17 ⁇ m.
  • the second silicon-based material meets (D v 90-D v 10)/D v 50 being 0.7 to 1.3, and optionally being 0.8 to 1.2.
  • (D v 90-D v 10)/D v 50 of the second silicon-based material falling within the foregoing range, the packing performance of the second silicon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the second silicon-based material is 0.6 m 2 /g to 1.6 m 2 /g, and optionally 0.7 m 2 /g to 1.5 m 2 /g. With the specific surface area ofthe second silicon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby also enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the second silicon-based material under 50000 N is 1.2 g/cm 3 to 1.8 g/cm 3 , and optionally 1.3 g/cm 3 to 1.7 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the second silicon-based material is 1.1 g/cm 3 to 1.7 g/cm 3 , and optionally 1.2 g/cm 3 to 1.6 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a powder resistivity of the second silicon-based material under 4 MPa is ⁇ 5 ⁇ cm, and optionally 0.3 ⁇ cm to 4 ⁇ cm.
  • a proportion of the second silicon-based material in the second active material by mass is ⁇ 15%, and optionally 3% to 10%.
  • the second silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, and silicon alloy material.
  • an intermediate region located between the first region and the second region includes the first active material and/or the second active material.
  • a porosity of the negative electrode film layer is ⁇ 15%, and optionally 20% to 45%. This helps the negative electrode film layer to have both high capacity and suitable pore structure, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • a compacted density of the negative electrode film layer is ⁇ 1.5 g/cm 3 , and optionally, 1.6 g/cm 3 to 1.8 g/cm 3 . This helps the negative electrode film layer to have both high capacity and good ion and electron transport performance, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • a surface density of the negative electrode film layer is ⁇ 7 mg/cm 2 , and optionally, 9 mg/cm 2 to 30 mg/cm 2 . This helps the negative electrode film layer to have both high capacity and good ion and electron transport performance, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • a second aspect of this application provides an electric apparatus, including the secondary battery according to the first aspect of this application.
  • the electric apparatus in this application includes the secondary battery provided in this application, and therefore has at least advantages that are the same as those of the secondary battery.
  • Ranges disclosed in this application are defined in the form of lower and upper limits.
  • a given range is defined by one lower limit and one upper limit selected, where the selected lower and upper limits define boundaries of that special range. Ranges defined in this way may or may not include end values, and any combination may be used, meaning that any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are provided for a specific parameter, it is understood that ranges of 60-110 and 80-120 can also be envisioned.
  • low limit values of a range are given as 1 and 2
  • upper limit values of the range are given as 3, 4, and 5, the following ranges can all be envisioned: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.
  • a value range of "a-b” is a short representation of any combination of real numbers between a and b, where both a and b are real numbers.
  • a value range of "0-5" means that all real numbers in the range of "0-5" are listed herein and "0-5" is just a short representation of combinations of these values.
  • a parameter expressed as an integer greater than or equal to 2 is equivalent to disclosure that the parameter is, such as, an integer among 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on.
  • a method including steps (a) and (b) indicates that the method may include steps (a) and (b) performed in order or may include steps (b) and (a) performed in order.
  • the foregoing method may further include step (c), which indicates that step (c) may be added to the method in any ordinal position, for example, the method may include steps (a), (b), and (c), steps (a), (c), and (b), steps (c), (a), and (b), or the like.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any one of the following conditions satisfies the condition "A or B”: A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).
  • a plurality of means two or more than two and the term "a plurality of types" means two types or more than two types.
  • the negative electrode plate is an important component of the secondary battery, and its performance is crucial to the performance of the secondary battery.
  • graphite is the most commonly used negative electrode active material.
  • the silicon-based materials have the advantage of high theoretical energy density, which can significantly increase the energy density of the secondary battery.
  • the intrinsic high electronic resistivity of silicon-based materials leads to rapid degradation of the reversible capacity of the secondary battery, and this degradation phenomenon is more severe at high rates.
  • the inventors have ingeniously improved the composition of the negative electrode film layer, enabling the secondary battery to have both good rate performance and cycling performance while having high energy density.
  • a first aspect of the embodiments of this application provides a secondary battery.
  • the secondary battery is not specifically limited to any particular type in this application.
  • the secondary battery may be a lithium-ion battery.
  • a secondary battery includes a positive electrode plate, a negative electrode plate, and an electrolyte. During charge and discharge of the secondary battery, ions are intercalated and deintercalated between the positive electrode plate and the negative electrode plate, and the electrolyte conducts the ions.
  • the electrolyte is not specifically limited to any particular type in this application, and may be selected depending on actual needs.
  • the electrolyte may be selected from at least one of solid electrolyte and liquid electrolyte (namely, an electrolyte solution).
  • a secondary battery using an electrolyte solution and some secondary batteries using a solid electrolyte may further include a separator, where the separator is arranged between the positive electrode plate and the negative electrode plate to mainly serve an isolation purpose.
  • FIG. 1 to FIG. 3 are schematic diagrams of an embodiment of a negative electrode plate according to this application.
  • a negative electrode plate 10 includes a negative electrode current collector 101 and a negative electrode film layer 102 formed on at least one surface of the negative electrode current collector 101.
  • the negative electrode film layer 102 has a first surface 102a far away from the negative electrode current collector 101 and a second surface 102b arranged opposite the first surface 102a.
  • the negative electrode film layer 102 has a thickness of denoted as H.
  • a region within a thickness range from the second surface 102b of the negative electrode film layer to 0.3H is denoted as a first region 1021 of the negative electrode film layer, and a region within a thickness range from the first surface 102a of the negative electrode film layer to 0.3H is denoted as a second region 1022 of the negative electrode film layer.
  • the first region 1021 includes a first active material
  • the second region 1022 includes a second active material.
  • the first active material includes a first carbon-based material and a first silicon-based material, the first carbon-based material includes primary particles, and the first silicon-based material includes secondary particles formed by aggregating primary particles.
  • the thickness H of the negative electrode film layer is a thickness of the negative electrode film layer on one side of the negative electrode current collector.
  • the first active material of the negative electrode film layer includes the first carbon-based material and the first silicon-based material, the first carbon-based material includes the primary particles, and the first silicon-based material includes the secondary particles formed by aggregating primary particles, so that the secondary battery can have both good rate performance and cycling performance while having high energy density.
  • the first active material of this application includes both the first carbon-based material and the first silicon-based material. Therefore, the first active material of this application has relatively high gram volume, and can achieve a higher energy density under the same surface density conditions.
  • the first carbon-based material includes primary particles, and the primary particles usually have relatively small specific surface area. This can reduce side reactions and improve the cycling performance of the secondary battery. Additionally, the primary particles have a relatively high capacity, which can increase the energy density of the secondary battery.
  • the first silicon-based material includes secondary particles, which can increase the ion intercalation channels of the first silicon-based material and help further optimize the rate performance of the secondary battery. Additionally, the silicon-based material being the secondary particles has poor compressive resistance. Thus, improving the structure of the negative electrode film layer can reduce the damage to the silicon-based material being the secondary particles by the rolling pressure, thereby giving full play to the advantage of the high capacity of the first silicon-based material.
  • the first active material includes the first silicon-based material
  • the first silicon-based material has a high capacity advantage, it can achieve higher energy density compared to conventional graphite negative electrodes under the same surface density conditions.
  • the first active material has relatively high resistance to ion liquid phase diffusion.
  • the first silicon-based material has relatively high electronic resistivity. Therefore, by making the first carbon-based material include primary particles and the first silicon-based material include secondary particles, it also helps improve the electronic conductivity of the negative electrode film layer, reduce battery polarization, and further optimize the rate performance and cycling performance of the secondary battery.
  • the primary particle and the secondary particle both have meanings well known in the art.
  • the primary particle is a particle in a non-agglomerated state.
  • the secondary particle is a particle in an agglomerated state that are formed through aggregation from two or more primary particles.
  • the primary particle and the secondary particle may be distinguished using scanning electron microscope (SEM) images.
  • the first carbon-based material may have a carbon enveloping layer on its surface.
  • the presence of the carbon enveloping layer may further increase the ion diffusion channels, accelerate the ion diffusion rate, and improve the electrical contact between the first carbon-based material and the first silicon-based material, which helps further optimize the rate performance of the secondary battery.
  • more than 80% of the surface of the first carbon-based material is covered with a carbon enveloping layer, and optionally 90% to 100% of the surface of the first carbon-based material is covered with a carbon enveloping layer.
  • the first carbon-based material may have a carbon enveloping layer on its surface, and the carbon enveloping layer includes hard carbon.
  • Hard carbon has the advantage of large interlayer spacing, which may accelerate the ion diffusion rate and thus may help further optimize the rate performance of the secondary battery.
  • the carbon enveloping layer on the surface of the first carbon-based material may be formed by carbonizing an organic carbon source.
  • the organic carbon source may be a carbon-containing material suitable for enveloping, as known in the art, for example, one or more of coal pitch, petroleum pitch, phenolic resin, and coconut shell.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number is ⁇ 70%, for example, ⁇ 72.5%, ⁇ 75%, ⁇ 77.5%, or ⁇ 80%.
  • the first carbon-based material including an appropriate proportion of primary particles can enable the first carbon-based material to have relatively high structural stability and further reduce the side reactions, and improve the cycling performance and/or rate performance of the secondary battery, and additionally can also increase the compacted density of the negative electrode film layer, thereby increasing the energy density of the secondary battery.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number should not be too high. In this case, if the compacted density of the first region of the negative electrode film layer is too high, it is easy to cause the overall porosity of the negative electrode film layer is prone to decrease, which in turn increases the internal resistance of the secondary battery and affects the further improvement of the rate performance and/or cycling performance of the secondary battery.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number may be 70% to 95%, 70% to 90%, 70% to 85%, 70% to 80%, 75% to 95%, 75% to 90%, 75% to 85%, or 75% to 80%. This is beneficial for the secondary battery to have both good cycling performance and rate performance as well as relatively high energy density.
  • the first carbon-based material may further include secondary particles, and a proportion of the first carbon-based material being the secondary particles in the first carbon-based material by number may be ⁇ 30%.
  • a proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number is ⁇ 55%, for example, ⁇ 57.5%, ⁇ 60%, ⁇ 62.5%, or ⁇ 65%.
  • the first silicon-based material includes an appropriate proportion of secondary particles, the ion intercalation channels in the first region of the negative electrode film layer can be increased, which is favorable for the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the rate performance of the secondary battery.
  • the proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number should not be too high. In this case, the secondary battery has more side reactions, which will affect the further improvement of the cycling performance of the secondary battery.
  • the proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number may be 55% to 90%, 60% to 90%, 65% to 90%, 55% to 85%, 60% to 85%, 65% to 85%, 55% to 80%, 60% to 80%, or 65% to 80%. This is beneficial for the secondary battery to have both good cycling performance and rate performance as well as relatively high energy density.
  • the first silicon-based material may also include primary particles (referring to particles in a non-agglomerated state herein), and the proportion of the first silicon-based material being the primary particles in the first silicon-based material by number may be ⁇ 45%.
  • the specific types of the first silicon-based material being the primary particles and the first silicon-based material being the secondary particles may be the same or may be different.
  • a porosity of the first silicon-based material being the secondary particles may be ⁇ 4%, and optionally 5% to 20%.
  • the porosity of the first silicon-based material being the secondary particles falling within the foregoing range, it helps improve the pore structure of the negative electrode film layer, improve the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby facilitating the acceleration of ion liquid phase transport speed; and it also helps increase the ion intercalation channels of the first silicon-based material, so that the ions quickly diffuse from the surface of the particles to the bulk phase, thereby facilitating further optimization of the rate performance of the secondary battery.
  • a particle size by volume D v 50 of the first carbon-based material may be 10 ⁇ m to 16 ⁇ m, and optionally 12 ⁇ m to 14 ⁇ m.
  • the particle size by volume D v 50 of the first carbon-based material falling within the foregoing range, it is favorable to improve the transport performance of ions and electrons, thereby further improving the rate performance of the secondary battery. In addition, it can also reduce the specific surface area of the first carbon-based material and reduce side reactions, thereby further improving the cycling performance of the secondary battery.
  • the inventors further found that when the first carbon-based material further meets one or more of the following conditions on the basis of the above-mentioned design, the performance of the secondary battery can be further improved. For example, at least one of the energy density, cycling performance, or rate performance of the secondary battery is further improved.
  • a particle size by volume D v 90 of the first carbon-based material may be 20 ⁇ m to 28 ⁇ m, and optionally 22 ⁇ m to 26 ⁇ m. With the particle size by volume D v 90 of the first carbon-based material falling within the foregoing range, the first carbon-based material particles have good consistency, which is conducive to improving the transport performance of ions and electrons, thereby further improving the rate performance of the secondary battery.
  • the first carbon-based material meets (D v 90-D v 10)/D v 50 being 0.8 to 1.6, and optionally being 1.1 to 1.4.
  • (D v 90-D v 10)/D v 50 of the first carbon-based material falling within the foregoing range, the packing performance of the first carbon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the first carbon-based material may be 1.0 m 2 /g to 1.8 m 2 /g, and optionally 1.2 m 2 /g to 1.6 m 2 /g. With the specific surface area of the first carbon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the first carbon-based material under 20000 N may be 1.75 g/cm 3 to 2.0 g/cm 3 , and optionally 1.8 g/cm 3 to 1.95 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the first carbon-based material may be 1.1 g/cm 3 to 1.3 g/cm 3 , and optionally 1.15 g/cm 3 to 1.25 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a degree of graphitization of the first carbon-based material may be ⁇ 93%, and optionally 94% to 96%. With the degree of graphitization of the first carbon-based material falling within the foregoing range, it helps improve the ion transport performance of the negative electrode film layer, so that the secondary battery can have both high energy density and good rate performance.
  • a gram volume of the first carbon-based material may be ⁇ 360 mAh/g, and optionally 361 mAh/g to 365 mAh/g. With the gram volume of the first carbon-based material falling within the foregoing range, the energy density of the secondary battery can be increased, and the carbon-based material can also be enabled to have good ion transport performance, which also helps improve the rate performance of the secondary battery.
  • a powder OI value of the first carbon-based material may be 5 to 15, and optionally 7 to 12.
  • the first carbon-based material has a relatively small powder OI value, so can quickly receive ions from the positive electrode, thereby further improving the rate performance of the secondary battery.
  • the first carbon-based material may include graphite, and optionally includes artificial graphite.
  • the first carbon-based material may include artificial graphite being secondary particles.
  • the proportion of the artificial graphite being primary particles in the first carbon-based material by number may be ⁇ 70%, ⁇ 72.5%, ⁇ 75%, ⁇ 77.5%, or ⁇ 80%.
  • a proportion of the artificial graphite being the primary particles in the first carbon-based material by number may be 70% to 95%, 70% to 90%, 70% to 85%, 70% to 80%, 75% to 95%, 75% to 90%, 75% to 85%, or 75% to 80%.
  • the first carbon-based material may include artificial graphite being primary particles, the artificial graphite being the primary particles has a carbon enveloping layer on its surface, and optionally, the carbon enveloping layer includes hard carbon.
  • a proportion of the first carbon-based material in the first active material by mass may be ⁇ 50%, and optionally 60% to 98%, 70% to 98%, 80% to 98%, 85% to 98%, 60% to 97%, 70% to 97%, 80% to 97%, or 85% to 97%.
  • the inventors further found that when the first silicon-based material meets one or more of the following conditions on the basis of the above-mentioned design, the performance of the secondary battery can be further improved, for example, at least one of the energy density, cycling performance, or rate performance of the secondary battery is further improved.
  • a particle size by volume D v 50 of the first silicon-based material may be 8 ⁇ m to 15 ⁇ m, and optionally 10 ⁇ m to 13 ⁇ m.
  • a particle size by volume D v 90 of the first silicon-based material may be 15 ⁇ m to 25 ⁇ m, and optionally 16 ⁇ m to 24 ⁇ m.
  • the ion intercalation channels in the negative electrode film layer can be increased, which is also favorable for the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the rate performance of the secondary battery.
  • the first silicon-based material meets (D v 90-D v 10)/D v 50 being 0.7 to 1.5, and optionally being 0.9 to 1.3.
  • (D v 90-D v 10)/D v 50 of the first silicon-based material falling within the foregoing range, the first silicon-based material particles has relatively good packing performance, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the first silicon-based material may be 0.7 m 2 /g to 2.0 m 2 /g, and optionally 0.8 m 2 /g to 1.6 m 2 /g.
  • the specific surface area of the first silicon-based material falling within the foregoing range, the ion intercalation channels of the negative electrode film layer can be increased, which is favorable for the rapid diffusion of ions from the particle surface to the bulk phase, thereby further optimizing the rate performance of the secondary battery.
  • the specific surface area ofthe first silicon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the first silicon-based material under 50000 N may be 1.0 g/cm 3 to 1.7 g/cm 3 , and optionally 1.2 g/cm 3 to 1.6 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the first silicon-based material may be 1.0 g/cm 3 to 1.5 g/cm 3 , and optionally 1.1 g/cm 3 to 1.4 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a powder resistivity of the first silicon-based material under 4 MPa may be ⁇ 15 ⁇ cm, and optionally 0.5 ⁇ cm to 12 ⁇ cm.
  • a proportion of the first silicon-based material in the first active material by mass is ⁇ 50%, and optionally 2% to 40%, 2% to 30%, 2% to 20%, 2% to 15%, 3% to 40%, 3% to 30%, 3% to 20%, or 3% to 15%.
  • the first silicon-based material may include one or more of elemental silicon, silicon oxide (SiO x , 0 ⁇ x ⁇ 2), silicon-carbon material, and silicon alloy material.
  • the silicon-carbon material is not specifically limited to any structure in this application.
  • high-energy ball milling may be used to disperse nano-silicon in a carbon material, disperse nano-silicon in porous carbon, disperse a carbon material in porous silicon, envelop a carbon material on the surface of nano-silicon, co-deposit nano-silicon and nano-carbon together.
  • the first silicon-based material may include secondary particles formed by aggregation of at least one of the following primary particles: silicon oxide material primary particles containing neither alkali metal nor alkaline earth metal, silicon oxide material primary particles containing either alkali metal or alkaline earth metal, silicon-carbon material primary particles, elemental silicon primary particles, and silicon alloy primary particles.
  • the alkali metal includes Li.
  • the alkaline earth metal includes Mg.
  • the first silicon-based material includes secondary particles formed by aggregation of silicon oxide material primary particles containing neither alkali metal nor alkaline earth metal, secondary particles formed by aggregation of silicon oxide material primary particles containing neither alkali metal nor alkaline earth metal and silicon oxide material primary particles containing either alkali metal or alkaline earth metal, secondary particles formed by aggregation of silicon oxide material primary particles containing either alkali metal or alkaline earth metal, secondary particles formed by aggregation of silicon-carbon material primary particles, secondary particles formed by aggregation of silicon-carbon material primary particles and silicon oxide material primary particles containing neither alkali metal nor alkaline earth metal, and secondary particles formed by aggregation of silicon-carbon material primary particles and silicon oxide material primary particles containing either alkali metal or alkaline earth metal.
  • the first silicon-based material has carbon enveloping layer on its surface.
  • the carbon enveloping layer may be arranged on the surface of elemental silicon, silicon oxide, or the like, to improve the electronic conductivity of the first silicon-based material and reduce the powder resistivity of the first silicon-based material.
  • the powder resistivity of the first silicon-based material may be adjusted by adjusting parameters such as the thickness of the carbon enveloping layer and the degree of graphitization.
  • the first silicon-based material may also have no carbon enveloping layer on its surface.
  • the powder resistivity of the first silicon-based material may be adjusted by adjusting parameters such as the structure of the silicon-carbon material and the percentage of element carbon.
  • the carbon enveloping layer on the surface of the first silicon-based material may be formed through chemical vapor deposition, pyrolysis, hydrothermal method, and the like.
  • the second region 1022 includes a second active material different from the first active material.
  • the second active material may include second carbon-based material.
  • the second carbon-based material may include secondary particles formed by aggregation of primary particles.
  • the ion transport speed can be accelerated, thereby further improving the rate performance of the secondary battery.
  • a proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number is ⁇ 60%, for example, ⁇ 62.5%, ⁇ 65%, ⁇ 67.5%, or ⁇ 70%.
  • the second carbon-based material includes an appropriate proportion of secondary particles, the ion intercalation channels in the first region of the negative electrode film layer can be increased, thereby further optimizing the rate performance of the secondary battery.
  • the proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number should not be too high. In this case, the secondary battery has more side reactions, which will affect the further improvement of the cycling performance of the secondary battery.
  • the proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number may be 60% to 90%, 60% to 85%, 60% to 80%, 60% to 75%, 65% to 90%, 65% to 85%, 65% to 80%, 65% to 75%, 70% to 90%, 70% to 85%, 70% to 80%, or 70% to 75%. This is favorable for the secondary battery to better have both good rate performance and good cycling performance.
  • the second carbon-based material may also include primary particles (referring to particles in a non-agglomerated state herein), and a proportion of the second carbon-based material being the primary particles in the second carbon-based material by number may be ⁇ 40%.
  • the second carbon-based material may have a carbon enveloping layer on its surface.
  • the presence of the carbon enveloping layer may increase the ion diffusion channels, which helps further optimize the rate performance of the secondary battery.
  • the second carbon-based material may have a carbon enveloping layer on its surface, and the carbon enveloping layer includes soft carbon.
  • Soft carbon has the advantage of large interlayer spacing, which may accelerate the ion diffusion rate and thus may help further optimize the rate performance of the secondary battery.
  • soft carbon has fewer structural defects, which may also reduce side reactions and enable the secondary battery to have good cycling performance.
  • the carbon enveloping layer on the surface of the second carbon-based material may be formed by carbonizing an organic carbon source.
  • the organic carbon source may be a carbon-containing material suitable for enveloping, as known in the art, for example, one or more of coal pitch, petroleum pitch, phenolic resin, and coconut shell.
  • the first carbon-based material has a carbon enveloping layer on its surface
  • the second carbon-based material has a carbon enveloping layer on its surface
  • a percentage of the carbon enveloping layer of the second carbon-based material by mass is greater than a percentage of the carbon enveloping layer of the first carbon-based material by mass
  • the rate performance of the secondary battery can be further improved; and by making the percentage of the carbon enveloping layer of the second carbon-based material by mass greater than the percentage of the carbon enveloping layer of the first carbon-based material by mass, ions can quickly migrate to the surface layer of the second carbon-based material, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a particle size by volume D v 50 of the second carbon-based material may be less than a particle size by volume D v 50 of the first carbon-based material.
  • the second region and the first region of the negative electrode film layer can have an ideal compacted density difference, so that the porosity in the thickness direction of the negative electrode film layer better matches the ion concentration distribution, which helps improve the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution and is favorable for ion transport, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a specific surface area of the second carbon-based material may be less than a specific surface area of the first carbon-based material.
  • a powder compacted density of the second carbon-based material under 20000 N may be less than a powder compacted density of the first carbon-based material under 20000 N.
  • the second region and the first region of the negative electrode film layer can have a good pore structure that better matches the concentration distribution of ions in the thickness direction of the negative electrode film layer, which improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution and is favorable for ion transport, thereby enabling the secondary battery to have better rate performance and cycling performance.
  • a tap density of the second carbon-based material may be less than a tap density of the first carbon-based material.
  • a degree of graphitization of the second carbon-based material may be lower than a degree of graphitization of the first carbon-based material.
  • the second carbon-based material has a relatively small degree of graphitization, so its interlayer spacing is relatively large, which is conducive to the rapid deintercalation of ions; and the first carbon-based material has a relatively high degree of graphitization, so its gram volume is relatively high. Therefore, by adjusting the degree of graphitization of the second carbon-based material to be lower than the degree of graphitization of the first carbon-based material, it is favorable for the secondary battery to have both high energy density and good rate performance.
  • a gram volume of the second carbon-based material may be less than a gram volume of the first carbon-based material.
  • a powder OI value of the second carbon-based material may be less than a powder OI value of the first carbon-based material.
  • the second carbon-based material has a relatively small powder OI value, and the particles have ion intercalation ports in all directions, so that ions from the positive electrode can be quickly received.
  • the inventors further found that when the second carbon-based material meets one or more of the following conditions on the basis of the above-mentioned design, the performance of the secondary battery can be further improved, for example, at least one of the energy density, cycling performance, or rate performance of the secondary battery is further improved.
  • a particle size by volume D v 50 of the second carbon-based material may be 9 ⁇ m to 15 ⁇ m, and optionally 11 ⁇ m to 13 ⁇ m.
  • a particle size by volume D v 90 of the second carbon-based material may be 20 ⁇ m to 26 ⁇ m, and optionally 21 ⁇ m to 25 ⁇ m.
  • the second carbon-based material meets (D v 90-D v 10)/D v 50 being 0.8 to 1.6, and optionally being 1.0 to 1.4.
  • (D v 90-D v 10)/D v 50 of the second carbon-based material falling within the foregoing range, the packing performance of the second carbon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the second carbon-based material is 0.5 m 2 /g to 1.5 m 2 /g, and optionally 0.7 m 2 /g to 1.2 m 2 /g. With the specific surface area ofthe second carbon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby also enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the second carbon-based material under 20000 N is 1.6 g/cm 3 to 1.8 g/cm 3 , and optionally 1.65 g/cm 3 to 1.75 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the second carbon-based material is 0.9 g/cm 3 to 1.2 g/cm 3 , and optionally 1.0 g/cm 3 to 1.1 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a degree of graphitization of the second carbon-based material may be ⁇ 92.5%, and optionally 93% to 94%. With the degree of graphitization of the second carbon-based material falling within the foregoing range, it helps improve the ion transport performance of the negative electrode film layer, so that the secondary battery can have both high energy density and good rate performance.
  • a gram volume of the second carbon-based material may be ⁇ 354 mAh/g, and optionally 355 mAh/g to 359 mAh/g. With the gram volume of the second carbon-based material falling within the foregoing range, the energy density of the secondary battery can be increased, and the carbon-based material can also be enabled to have good ion transport performance, which also helps improve the rate performance of the secondary battery.
  • the particle size by volume D v 50 of the second carbon-based material is denoted as A in ⁇ m
  • the specific surface area of the second carbon-based material is denoted as B in m 2 /g
  • A/B is 9.0 to 20, and optionally 11 to 15.
  • a powder OI value of the second carbon-based material may be 2 to 8, and optionally 4 to 6.
  • the second carbon-based material has a relatively small powder OI value, so can quickly receive ions from the positive electrode, thereby further improving the rate performance of the secondary battery.
  • the second carbon-based material may include graphite, and optionally includes artificial graphite.
  • the second carbon-based material may include artificial graphite being secondary particles.
  • the proportion of the artificial graphite being the secondary particles in the second carbon-based material by number may be ⁇ 60%, for example, ⁇ 62.5%, ⁇ 65%, ⁇ 67.5%, or ⁇ 70%.
  • the proportion of the artificial graphite being the secondary particles in the second carbon-based material by number may be 60% to 90%, 60% to 85%, 60% to 80%, 60% to 75%, 65% to 90%, 65% to 85%, 65% to 80%, 65% to 75%, 70% to 90%, 70% to 85%, 70% to 80%, or 70% to 75%.
  • the second carbon-based material may include artificial graphite being secondary particles, the artificial graphite has a carbon enveloping layer on its surface, and optionally, the carbon enveloping layer includes soft carbon.
  • a proportion of the second carbon-based material in the second active material by mass may be ⁇ 85%, and optionally 85% to 100%, 88% to 100%, 90% to 100%, 92% to 100%, 85% to 97%, 88% to 97%, 90% to 97%, or 92% to 97%. This helps improve the rate performance of the secondary battery.
  • a proportion of the second carbon-based material in the second active material by mass may be 100%.
  • the second active material may further include a second silicon-based material in addition to the second carbon-based material, which can further increase the energy density of the secondary battery.
  • the second silicon-based material may include one or more of primary particles and secondary particles formed by aggregation of primary particles, and optionally includes primary particles.
  • the second silicon-based material includes primary particles, and a proportion of the second silicon-based material being the primary particles in the second silicon-based material by number may be ⁇ 60%, and optionally 70% to 95%.
  • the second silicon-based material is mainly primary particles, it helps reduce the probability of particle breakage and increase the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery.
  • the second silicon-based material may further include secondary particles, and a proportion of the second silicon-based material being the secondary particles in the second silicon-based material by number may be ⁇ 40%.
  • the specific types of the second silicon-based material being the primary particles and the second silicon-based material being the secondary particles may be the same or may be different.
  • a proportion of the second silicon-based material in the second active material by mass may be less than a proportion of the first silicon-based material in the first active material by mass.
  • the second silicon-based material is in direct contact with the electrolyte solution.
  • a particle size by volume D v 50 of the second silicon-based material may be less than a particle size by volume D v 50 of the first silicon-based material.
  • the second silicon-based material is more affected by the pressure roller, making the particles more prone to breakage.
  • the probability of particle breakage of the second silicon-based material can be reduced, the electronic conductivity of the second silicon-based material can be increased, and the ion intercalation channel of the negative electrode film layer can be increased, thereby enabling the secondary battery to have both high energy density and good rate performance.
  • a specific surface area of the second silicon-based material may be less than a specific surface area of the first silicon-based material.
  • the specific surface area of the second silicon-based material helps reduce side reactions, thereby facilitating the secondary battery to have better cycling performance.
  • a powder compacted density of the second silicon-based material under 50000 N may be greater than a powder compacted density of the first silicon-based material under 50000 N.
  • a tap density of the second silicon-based material may be greater than a tap density of the first silicon-based material.
  • a powder resistivity of the second silicon-based material under 4 MPa may be less than a powder resistivity of the first silicon-based material under 4 MPa.
  • the inventors further found that when the second silicon-based material meets one or more of the following conditions on the basis of the above-mentioned design, the performance of the secondary battery can be further improved, for example, at least one of the energy density, cycling performance, or rate performance of the secondary battery is further improved.
  • a particle size by volume D v 50 of the second silicon-based material may be 4 ⁇ m to 12 ⁇ m, and optionally 5 ⁇ m to 11 ⁇ m.
  • a particle size by volume D v 90 of the second silicon-based material may be 8 ⁇ m to 18 ⁇ m, and optionally 9 ⁇ m to 17 ⁇ m.
  • the second silicon-based material meets (D v 90-D v 10)/D v 50 being 0.7 to 1.3, and optionally being 0.8 to 1.2.
  • (D v 90-D v 10)/D v 50 of the second silicon-based material falling within the foregoing range, the packing performance of the second silicon-based material particles is relatively good, which is conducive to increasing the compacted density of the negative electrode film layer, thereby further increasing the energy density of the secondary battery; and additionally, it is also favorable for the negative electrode film layer to have a suitable pore structure, thereby further improving the rate performance of the secondary battery.
  • a specific surface area of the second silicon-based material may be 0.6 m 2 /g to 1.6 m 2 /g, and optionally 0.7 m 2 /g to 1.5 m 2 /g. With the specific surface area ofthe second silicon-based material falling within the foregoing range, it is conducive to reducing side reactions, thereby also enabling the secondary battery to have better cycling performance.
  • a powder compacted density of the second silicon-based material under 50000 N is 1.2 g/cm 3 to 1.8 g/cm 3 , and optionally 1.3 g/cm 3 to 1.7 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a tap density of the second silicon-based material may be 1.1 g/cm 3 to 1.7 g/cm 3 , and optionally 1.2 g/cm 3 to 1.6 g/cm 3 .
  • the compacted density of the negative electrode film layer can be increased, thereby further increasing the energy density of the secondary battery; and it is also favorable for the negative electrode film layer to have a suitable pore structure, which improves transport performance of ions and electrons, and improves the wettability and retention characteristics of the negative electrode film layer with respect to the electrolyte solution, thereby further improving the rate performance and/or cycling performance of the secondary battery.
  • a powder resistivity of the second silicon-based material under 4 MPa may be ⁇ 5 ⁇ cm, and optionally 0.3 ⁇ cm to 4 ⁇ cm.
  • the second silicon-based material may include one or more of elemental silicon, silicon oxide (SiO x , 0 ⁇ x ⁇ 2), silicon-carbon material, and silicon alloy material.
  • the silicon-carbon material is not specifically limited to any structure in this application.
  • high-energy ball milling may be used to disperse nano-silicon in a carbon material, disperse nano-silicon in porous carbon, disperse a carbon material in porous silicon, envelop a carbon material on the surface of nano-silicon, co-deposit nano-silicon and nano-carbon together.
  • the second silicon-based material may have a carbon enveloping layer on its surface.
  • the carbon enveloping layer may be arranged on the surface of elemental silicon, silicon oxide, or the like, to improve the electronic conductivity of the second silicon-based material and reduce the powder resistivity.
  • the powder resistivity of the second silicon-based material can be adjusted.
  • the surface of the second silicon-based material may alternatively have no carbon enveloping layer.
  • the powder resistivity of the second silicon-based material can be adjusted.
  • the carbon enveloping layer on the surface of the second silicon-based material may be formed through chemical vapor deposition, pyrolysis, hydrothermal method, and the like.
  • the first active material includes a first carbon-based material and a first silicon-based material.
  • the first carbon-based material includes primary particles, and the first carbon-based material has a carbon enveloping layer on its surface.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number is ⁇ 70%, and optionally 75% to 90%.
  • the first silicon-based material includes secondary particles formed by aggregation of primary particles.
  • a proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number is ⁇ 55%, and optionally 60% to 85%.
  • the second active material includes a second carbon-based material.
  • the second carbon-based material includes secondary particles formed by aggregation of primary particles.
  • a proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number is ⁇ 60%, and optionally, 70% to 85%.
  • the second carbon-based material has a carbon enveloping layer on its surface.
  • the first active material includes a first carbon-based material and a first silicon-based material.
  • the first carbon-based material includes primary particles, and the first carbon-based material has a carbon enveloping layer on its surface.
  • a proportion of the first carbon-based material being the primary particles in the first carbon-based material by number is ⁇ 70%, and optionally 75% to 90%.
  • the first silicon-based material includes secondary particles formed by aggregation of primary particles.
  • a proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number is ⁇ 55%, and optionally 60% to 85%.
  • the second active material includes a second carbon-based material and a second silicon-based material.
  • the second carbon-based material includes secondary particles formed by aggregation of primary particles.
  • a proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number is ⁇ 60%, and optionally, 70% to 85%.
  • the second carbon-based material has a carbon enveloping layer on its surface.
  • the second silicon-based material includes primary particles, and a proportion of the second silicon-based material being the primary particles in the second silicon-based material by number is ⁇ 60%, and optionally, 70% to 95%.
  • the intermediate region 1023 includes the first active material and/or the second active material.
  • the intermediate region 1023 may be the same as the first region 1021 in composition.
  • a distribution region of the first active material in the thickness direction of the negative electrode film layer 102 is within a thickness range from a second surface 102b of the negative electrode film layer to 0.7H.
  • the intermediate region 1023 may be the same as the second region 1022 in composition.
  • a distribution region of the second active material in the thickness direction of the negative electrode film layer 102 is within a thickness range from a first surface 102a of the negative electrode film layer to 0.7H.
  • FIG. 1 the intermediate region 1023 may be the same as the first region 1021 in composition.
  • a distribution region of the first active material in the thickness direction of the negative electrode film layer 102 is within a thickness range from a second surface 102b of the negative electrode film layer to 0.7H.
  • the intermediate region 1023 may be the same as the second region 1022 in composition.
  • the first region 1021 of the negative electrode film layer may also include other negative electrode active materials known in the art in addition to the first carbon-based material and the first silicon-based material, for example, may also include one or more of tin-based material and lithium titanate.
  • the second region 1022 of the negative electrode film layer may also include other negative electrode active materials known in the art in addition to the second carbon-based material and the second silicon-based material, for example, may also include one or more of tin-based material and lithium titanate.
  • the intermediate region 1023 of the negative electrode film layer may also include one or more of tin-based material and lithium titanate.
  • the first region, the second region, and the intermediate region of the negative electrode film layer may optionally include a negative electrode conductive agent and/or a negative electrode binder.
  • the negative electrode conductive agent is not limited to a particular type in this application.
  • the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofiber.
  • the negative electrode binder is not limited to a particular type in this application.
  • the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resin (for example, polyacrylic acid PAA, polymethylacrylic acid PMAA, and polyacrylic acid sodium PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • SR-1B water-soluble unsaturated resin
  • PAAS waterborne acrylic resin
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • CMCS carboxymethyl chitosan
  • the first region, the second region, and the intermediate region of the negative electrode film layer may optionally include other additives.
  • the another additive may include a thickener, for example, sodium carboxymethyl cellulose (CMC) or PTC thermistor material.
  • a porosity of the negative electrode film layer may be ⁇ 15%, and optionally 20% to 45%. This helps the negative electrode film layer to have both high capacity and suitable pore structure, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • a compacted density of the negative electrode film layer may be ⁇ 1.5 g/cm 3 , and optionally, 1.6 g/cm 3 to 1.8 g/cm 3 . This helps the negative electrode film layer to have both high capacity and good ion and electron transport performance, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • a surface density of the negative electrode film layer may be ⁇ 7 mg/cm 2 , and optionally, 9 mg/cm 2 to 30 mg/cm 2 . This helps the negative electrode film layer to have both high capacity and good ion and electron transport performance, which in turn helps the secondary battery to have both high energy density and good cycling performance and rate performance.
  • the negative electrode current collector may be a metal foil current collector or a composite current collector.
  • a copper foil may be used as the metal foil.
  • the composite current collector may include a polymer material matrix and a metal material layer formed on at least one surface of the polymer material matrix.
  • the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material matrix may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).
  • the negative electrode plate does not exclude additional functional layers other than the negative electrode film layer.
  • the negative electrode plate of this application further includes a conductive primer layer (for example, consisting of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and arranged on the surface of the negative electrode current collector.
  • the negative electrode plate of this application further includes a protective layer covering the surface of the negative electrode film layer.
  • the negative electrode current collector includes two opposite surfaces in its thickness direction, and the negative electrode film layer is arranged on either or both of the two opposite surfaces of the negative electrode current collector.
  • the various parameters of the negative electrode film layer given in this application are parameters of the negative electrode film layer on one side of the negative electrode current collector.
  • the negative electrode film layer is arranged on two sides of the negative electrode current collector, parameters of the negative electrode film layer on any one side meet this application, that is, are considered to fall within the protection scope of this application.
  • the presence of a carbon enveloping layer on a surface of the material may be determined by transmission electron microscope.
  • the particle sizes by volume D v 10, D v 50, and D v 90 of the material have meanings well known in the art, represent the particle sizes corresponding to the cumulative volume distribution percentages of 10%, 50%, and 90%, respectively, and may be tested using an instrument and a method known in the art.
  • the particle size by volume may be determined using a laser particle size analyzer in accordance with GB/T 19077-2016.
  • the test instrument may be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments in UK.
  • the specific surface area of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art.
  • the specific surface area may be measured according to GB/T 19587-2017 using the nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method.
  • the test instrument may be a specific surface area and pore size analyzer of Tri-Star 3020 from Micromeritics of USA.
  • the powder compacted density of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art. For example, it can be measured in accordance with the standard GB/T 24533-2009 by using an electronic pressure testing machine (for example, electronic pressure testing machine of model UTM7305).
  • An example test method is as follows: weighing 1 g of sample powder and adding it to a mold with a base area of 1.327 cm 2 , applying pressure to the required level and holding the pressure for 30s, next releasing the pressure and holding for 10s, and then recording the data and calculating the powder compacted density of the material under the required pressure.
  • the tap density of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art.
  • the tap density may be measured in accordance with GB/T 5162-2006 using a powder tap density tester.
  • the test instrument may be Dandong Bettersize BT-301, with the test parameters as follows: 250 ⁇ 15 times/min, amplitude: 3 ⁇ 0.2 mm, vibration frequency: 5000 times, and measuring cylinder: 25 mL.
  • the degree of graphitization of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art.
  • an X-ray diffractometer for example, Bruker D8 Discover
  • d 002 is the average interlayer spacing of the C(002) crystal plane in the crystal structure of the material, expressed in nanometers (nm).
  • the powder OI value of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art.
  • an X-ray diffractometer for example, Bruker D8 Discover
  • I 004 is the integrated area of the diffraction peak of the crystalline carbon 004 crystal plane in the powder sample
  • I 110 is the integrated area of the diffraction peak of the crystalline carbon 110 crystal plane in the powder sample.
  • a copper target may be used as an anode target
  • a CuK ⁇ ray is used as a radiation source
  • a ray wavelength ⁇ 1.5418 ⁇
  • a scanning angle 2 ⁇ is 20° to 80°
  • a scanning rate is 4°/min.
  • the powder resistivity of the material has a meaning well known in the art, and may be tested using an instrument and a method known in the art.
  • the powder resistivity may be tested using a resistivity tester (for example, ST2722 powder resistivity tester from Suzhou Jingge Electronics Co., Ltd.).
  • a resistivity tester for example, ST2722 powder resistivity tester from Suzhou Jingge Electronics Co., Ltd.
  • 1 g of powder sample is taken and placed between the electrodes of the resistivity tester, an electronic press is used to apply constant pressure on the sample to the test pressure (for example, 4 MPa) and maintain at this pressure for 15s to 25s to obtain a sheet-shaped sample.
  • the gram volume of the material has a meaning well known in the art, and may be tested using a method known in the art.
  • the exemplary test method is as follows: the sample powder, a conductive agent carbon black (Super P), and a binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 91.6:1.8:6.6 in a solvent N-methylpyrrolidone (NMP) to prepare a slurry; the prepared slurry is applied on a surface of a negative electrode current collector copper foil, and the copper foil coated with the slurry is dried in an oven for reserve use; ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to prepare an organic solvent, and LiPF 6 is dissolved in the preceding organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L; next, a metal lithium sheet
  • the compacted density of the negative electrode film layer has a meaning well known in the art, and may be tested using a method known in the art.
  • the compacted density of the negative electrode film layer the surface density of the negative electrode film layer/a thickness of the negative electrode film layer.
  • the thickness of the negative electrode film layer has a meaning well known in the art, and may be tested using a method known in the art, such as a micrometer (for example, Mitutoyo 293-100 model, with an accuracy of 0.1 ⁇ m).
  • the porosity of the negative electrode film layer has a meaning well known in the art, and may be tested using a method known in the art.
  • An example test method is as follows: A single-side coated and cold-pressed negative electrode plate (for a negative electrode plate coated with the negative electrode film layer on two sides, the negative electrode film layer on any one side may be wiped off first) is taken and punched into small round samples. An apparent volume V 1 of the negative electrode plate is calculated. In accordance with GB/T 24586-2009, with an inert gas (such as helium or nitrogen) served as the medium, a true volume V 2 of the negative electrode plate is tested using a true density tester through a gas displacement method.
  • an inert gas such as helium or nitrogen
  • the porosity of the negative electrode film layer (V 1 -V 2 )/V 1 ⁇ 100%.
  • a plurality of (for example, 30) negative electrode plate samples with good appearance and no edge flaking may be taken for the test, and results are averaged, thereby improving accuracy of a test result.
  • the test instrument may be a true density tester of model AccuPyc II 1340 from Micromeritics.
  • the porosity of the first silicon-based material being the secondary particles may be tested using a method known in the art.
  • the true density ⁇ r of the first silicon-based material being the secondary particles may be tested using a true density tester (for example, AccuPyc II 1340).
  • tests for various parameters of the first active material, second active material, or negative electrode film layer mentioned above may be conducted by sampling and testing from the prepared secondary battery according to the following steps.
  • Discharging the secondary battery for sake of safety, generally making the secondary battery in fully discharged state
  • disassembling the secondary battery taking out the negative electrode plate, and using dimethyl carbonate to soak the negative electrode plate for a specific time (for example, 2 h to 10 h); and taking out the negative electrode plate and drying it at a given temperature for a specific time (for example, 60°C, for more than 4 h), and taking out the negative electrode plate obtained after drying.
  • the samples from the dried negative electrode plate may be tested for parameters related to the negative electrode film layer described above, for example, surface density, compacted density, and porosity.
  • the dried negative electrode plate is baked at a certain temperature and time (for example, 400°C, for more than 2 h).
  • a region of the baked negative electrode plate is randomly selected for sampling the second active material first (sampling may be done by scraping powder with a blade), with the sampling position being the second region of the negative electrode film layer.
  • the first active material is sampled in the same manner, and the sampling position is the first region of the negative electrode film layer.
  • the collected first active material and second active material are sieved respectively (for example, sieved with a 200-mesh sieve).
  • the first active material and second active material samples that can be used for testing the parameters of the above-mentioned materials of this application are obtained.
  • a method for measuring the proportion of the first carbon-based material being the primary particles in the first carbon-based material by number may be as follows: laying and sticking the first active material on a conductive adhesive to make a sample under test of 6 cm ⁇ 1.1 cm; and using a scanning electron microscope to measure the particle morphology in accordance with JY/T010-1996.
  • a plurality of (for example, 10) different regions in samples under test may be randomly selected for scanning test, and with a specified magnification (for example, 500 times or 1000 times), a ratio of the number of first carbon-based material being the primary particles to a total number of the first carbon-based material in each of the test regions is calculated.
  • test result An average of the calculated results of the plurality of test regions is taken as the test result.
  • a plurality of (for example, 5 or 10) test samples may also be prepared to repeat the foregoing test, and an average of the test samples is taken as a final test result.
  • the proportion of the first silicon-based material being the secondary particles in the first silicon-based material by number may also be tested.
  • a method for measuring the proportion of the second carbon-based material being the secondary particles in the second carbon-based material by number may be as follows: laying and sticking the second active material on a conductive adhesive to make a sample under test of 6 cm ⁇ 1.1 cm; and using a scanning electron microscope to measure the particle morphology in accordance with JY/T010-1996.
  • a plurality of (for example, 10) different regions in samples under test may be randomly selected for scanning test, and with a specified magnification (for example, 500 times or 1000 times), a ratio of the number of second carbon-based material being the secondary particles to a total number of the second carbon-based material in each of the test regions is calculated.
  • test result An average of the calculated results of the plurality of test regions is taken as the test result.
  • a plurality of (for example, 5 or 10) test samples may also be prepared to repeat the foregoing test, and an average of the test samples is taken as a final test result.
  • proportion of the second silicon-based material being the primary particles in the second silicon-based material by number may also be tested.
  • the proportions of primary particles (referring to particles in a nonagglomerated state herein) and secondary particles in the carbon-based material (for example, the first carbon-based material or the second carbon-based material) by number may be adjusted using a method known in the art.
  • the proportions of primary particles and secondary particles by number may be adjusted by adjusting the preparation parameters (for example, type of coke raw material, shaping process, granulation process, type and amount of granulating agent).
  • the proportions of the primary particles and the secondary particles by number may be adjusted by adjusting a mixing ratio of the graphite primary particles to the graphite secondary particles.
  • the proportions of primary particles (referring to particles in a nonagglomerated state herein) and secondary particles in the silicon-based material (for example, the first silicon-based material or the second silicon-based material) by number may be adjusted using similar methods.
  • the proportions of primary particles and secondary particles by number may be adjusted by adjusting the preparation parameters (for example, type of raw material, granulation process, type and amount of granulating agent).
  • the proportions of the primary particles and the secondary particles by number may be adjusted by adjusting a mixing ratio of the silicon-based material being the primary particles to the silicon-based material being the secondary particles.
  • This application further provides a method for preparing the negative electrode plate of this application.
  • the method includes the following steps: providing a first slurry containing a first active material and a second slurry containing a second active material; applying the first slurry on a negative electrode current collector, applying the second slurry on the first slurry, and drying and cold pressing the negative electrode current collector coated with the first slurry and the second slurry to obtain a negative electrode plate.
  • the second active material, an optional conductive agent, an optional binder, and other optional auxiliary agents may be dispersed in a solvent (for example, deionized water) to form the second slurry.
  • a solvent for example, deionized water
  • the second active material includes the second carbon-based material, or a mixture of the second carbon-based material and the second silicon-based material.
  • the first slurry and the second slurry may be applied simultaneously or applied separately in two times. In some embodiments, the first slurry and the second slurry are applied simultaneously. Simultaneous application can reduce the resistance of the negative electrode film layer, thereby further improving the rate performance and cycling performance of the secondary battery.
  • the application weight of the first slurry and the second slurry may be adjusted based on actual conditions.
  • the first active material, second active material, and the like mentioned above may be commercially obtained or prepared using the following methods in this application.
  • a silicon-based material being the secondary particles may be prepared using the following method: preparing a solution containing primary particles, binder, and solvent, and performing spray drying on the solution to obtain the silicon-based material being the secondary particles.
  • the binder is not specifically limited, and specific examples thereof may include one or more of asphalt, starch, phenolic resin, polyvinyl alcohol, epoxy resin, perchlorovinyl resin, and butyl rubber.
  • the solvent is not specifically limited provided that it allows the primary particles to be fully dispersed.
  • the types of primary particles used may be the same or different.
  • a carbon-based material being the primary particles may be prepared using the following method: crushing and shaping a coke raw material, and performing graphitization treatment to obtain the carbon-based material being the primary particles.
  • a specific example of the coke raw material may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.
  • the graphitization temperature may range from 2800°C to 3200°C.
  • a carbon-based material being the secondary particles may be prepared using the following method: crushing and shaping a coke raw material, mixing the material with a binder for granulation, and performing graphitization treatment to obtain the carbon-based material being the secondary particles.
  • a specific example of the coke raw material may include one or more of petroleum coke, needle coke, pitch coke, and metallurgical coke.
  • the graphitization temperature may range from 2800°C to 3200°C.
  • a specific example of the binder may include asphalt.
  • the above preparation process does not include the step of forming a carbon enveloping layer on a surface of the material.
  • the carbon enveloping layer on the surface of the carbon-based material may be formed by carbonizing an organic carbon source.
  • the organic carbon source may be a carbon-containing material suitable for enveloping, as known in the art, for example, one or more of coal pitch, petroleum pitch, phenolic resin, and coconut shell.
  • the carbon enveloping layer on the surface of the silicon-based material may be formed through chemical vapor deposition, pyrolysis, hydrothermal method, and the like.
  • the positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.
  • the positive electrode current collector has two opposite surfaces in its thickness direction, and the positive electrode film layer is arranged on either or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer typically includes a positive electrode active material, an optional binder, and an optional conductive agent.
  • the positive electrode film layer is typically formed by applying a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing.
  • the positive electrode slurry is typically formed by dispersing the positive electrode active material, the optional conductive agent, the optional binder, and any other components in a solvent and stirring them to uniformity.
  • the solvent may be but is not limited to N-methylpyrrolidone (NMP).
  • the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylenehexafluoropropylene copolymer, and fluorine-containing acrylic resin.
  • the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofiber.
  • the positive electrode active material may be a positive electrode active material for secondary batteries well known in the art.
  • the positive electrode active material used for the lithium-ion battery may include but is not limited to one or more of lithium transition metal oxide, lithium-containing phosphate, and respective modified compounds thereof.
  • the lithium transition metal oxide may include but are not limited to one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and respective modified compounds thereof.
  • lithium-containing phosphate may include but are not limited to one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and respective modified compounds thereof.
  • the positive electrode active material used for the lithium-ion battery may include one or more of lithium transition metal oxide with a general formula Li a Ni b Co c M d O e A f and modified compounds thereof, where 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.
  • lithium transition metal oxide with a general formula Li a Ni b Co c M d O e A f and modified compounds thereof, where 0.8 ⁇ a ⁇ 1.2, 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from
  • the positive electrode active material used for the lithium-ion battery may include one or more of LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1 /3 Mn 1/3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO 4 , and LiMnPO 4 .
  • LiCoO 2 LiNiO 2 , LiMnO 2 , LiMn 2 O 4
  • NCM333 LiNi 1/3 Co 1 /3 Mn 1/3 O 2
  • NCM523 LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • NCM622 LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • NCM811 LiNi 0.85 Co 0.15 Al
  • the foregoing modified compounds of the positive electrode active material may be obtained through doping modification and/or surface coating modification on the positive electrode active material.
  • the electrolyte is an electrolyte solution
  • the electrolyte solution includes an electrolytic salt and a solvent.
  • the electrolytic salt is not limited to a specific type, and may be selected based on actual needs.
  • the electrolytic salt may include one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethane)sulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluoro bis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro oxalato phosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • the solvent is not limited to a specific type, and may be selected based on actual needs.
  • the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), gammabutyrolactone (GBL), sulfolane (SF), methyl sulfonyl methane (MS
  • the electrolyte solution further optionally includes an additive.
  • the additive may include a negative electrode film-forming additive, or may include a positive electrode film-forming additive, or may include an additive capable of improving some performance of the secondary battery, for example, an additive for improving overcharge performance of the secondary battery, an additive for improving high-temperature performance of the secondary battery, or an additive for improving low-temperature power performance of the secondary battery.
  • the separator is not limited to a particular type in this application, and may be any well-known porous separator with good chemical stability and mechanical stability.
  • the separator may be made of one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.
  • the separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, all layers may be made of the same or different materials.
  • the positive electrode plate, the separator, and the negative electrode plate may be made into an electrode assembly through winding or lamination.
  • the secondary battery may include an outer package.
  • the outer package may be used for packaging the foregoing electrode assembly and electrolyte.
  • the outer package may be a hard shell, for example, a hard plastic shell, an aluminum shell, or a steel shell.
  • the outer package may alternatively be a soft package, for example, a soft bag.
  • Material of the soft package may be plastic, for example, one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 4 shows a rectangular secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover plate 53.
  • the housing 51 may include a base plate and a side plate connected to the base plate, and the base plate and the side plate enclose an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is configured to cover the opening to close the accommodating cavity.
  • the positive electrode plate, the negative electrode plate, and the separator may be made into an electrode assembly 52 through winding or lamination.
  • the electrode assembly 52 is packaged in the accommodating cavity.
  • the electrolyte solution infiltrates the electrode assembly 52.
  • the secondary battery 5 may include one or more electrode assemblies 52 whose quantity is adjustable as required.
  • the positive electrode plate, the separator, the negative electrode plate, and the electrolyte solution may be assembled to form a secondary battery.
  • the positive electrode plate, the separator, and the negative electrode plate may be made into an electrode assembly through winding or lamination; and the electrode assembly is placed into an outer package, followed by drying, and the electrolyte solution is injected, followed by processes such as vacuum packaging, standing, formation, and shaping, to obtain the secondary battery.
  • such secondary batteries of this application may be assembled into a battery module.
  • the battery module may include a plurality of secondary batteries whose quantity may be adjusted based on application and capacity of the battery module.
  • FIG. 6 is a schematic diagram of a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be sequentially arranged along a length direction of the battery module 4.
  • the batteries may alternatively be arranged in any other manners.
  • the plurality of secondary batteries 5 may be fastened using fasteners.
  • the battery module 4 may further include a housing with an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.
  • the battery modules may be further assembled into a battery pack, and a quantity of battery modules included in the battery pack may be adjusted based on application and capacity of the battery pack.
  • FIG. 7 and FIG. 8 are schematic diagrams of a battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3.
  • the upper box body 2 is configured to be engaged with the lower box body 3 to form an enclosed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 may be arranged in the battery box in any manner.
  • An embodiment of this application further provides an electric apparatus.
  • the electric apparatus includes at least one of the secondary battery, the battery module, or the battery pack in this application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electric apparatus or an energy storage unit of the electric apparatus.
  • the electric apparatus may be but is not limited to a mobile device (for example, a mobile phone, a tablet computer, or a notebook computer), an electric vehicle (for example, a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicle, or an electric truck), an electric train, a ship, a satellite, and an energy storage system.
  • the secondary battery, the battery module, or the battery pack may be selected for the electric apparatus based on requirements for using the electric apparatus.
  • FIG. 9 is a schematic diagram of an electric apparatus as an example.
  • This electric apparatus is a battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • a battery pack or a battery module may be used.
  • the electric apparatus may be a mobile phone, a tablet computer, a notebook computer, or the like.
  • Such electric apparatus is generally required to be light and thin and may use a secondary battery as its power source.
  • the first carbon-based material of Example 4 was primary particles, which could be commercially obtained or prepared using the following method: crushing and shaping the petroleum coke, then performing graphitization treatment in the range of 2800°C to 3200°C, cooling to room temperature, and obtaining the product after sieving.
  • the first carbon-based material and the second carbon-based material might be commercially obtained, or might be prepared using the following method: crushing and shaping the petroleum coke, next mixing it with a binder asphalt and granulating them, then performing graphitization treatment in the range of 2800°C to 3200°C, cooling to room temperature, and obtaining the product after sieving.
  • the proportions of primary particles and secondary particles in the first carbon-based material (second carbon-based material) by number might be modified by adjusting the preparation process parameters (for example, shaping process, granulation process, type and amount of asphalt); or the proportions of primary particles and secondary particles by number might be adjusted by modifying a mixing ratio of the first carbon-based material (second carbon-based material) being the primary particles and the first carbon-based material (second carbon-based material) being the secondary particles.
  • the carbon enveloping layers on the surfaces of the first carbon-based material and the second carbon-based material might be formed by mixing the graphitized material with petroleum pitch and then carbonizing the resulting mixture.
  • the first silicon-based material of Comparative Example 1 was primary particles, and could be commercially obtained.
  • the silicon-based material being the secondary particles might be immersed in a high-temperature molten filler, pressurized to control the degree of filler filling, and then subjected to high-temperature carbonization to adjust the porosity.
  • the carbon enveloping layer on the surface of pre-intercalated lithium silicon oxide might be formed through chemical vapor deposition.
  • the first active material (as shown in Table 1), a conductive agent Super P, carbon nanotubes (CNTs), a binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose were mixed at a weight ratio of 96.2:0.7:0.1:1.8:1.2 in an appropriate amount of deionized water solvent, and the resulting mixture was stirred thoroughly to form a first slurry.
  • the sum of the proportions of the secondary particles and the primary particles in the first carbon-based material by number was 100%, and the sum of the proportions of the secondary particles and the primary particles in the first silicon-based material by number was 100%. Therefore, the proportion of the secondary particles or the primary particles by number might be calculated based on the proportion of the primary particles or the secondary particles by number in Table 1.
  • the second active material (as shown in Table 2), a conductive agent Super P, carbon nanotubes (CNTs), a binder styrene-butadiene rubber, and a thickener sodium carboxymethyl cellulose were mixed at a weight ratio of 96.2:0.7:0.1:1.8:1.2 in an appropriate amount of deionized water solvent, and the resulting mixture was stirred thoroughly to form a second slurry.
  • the sum of the proportions of the secondary particles and the primary particles in the second carbon-based material by number was 100%, and the sum of the proportions of the secondary particles and the primary particles in the second silicon-based material by number was 100%. Therefore, the proportion of the secondary particles or the primary particles by number might be calculated based on the proportion of the primary particles or the secondary particles by number in Table 2.
  • the first slurry and the second slurry were simultaneously extruded through a dual-chamber coating device.
  • the first slurry was applied onto two surfaces of a negative electrode current collector copper foil, the second slurry was applied onto the first slurry, followed by drying and cold pressing, to obtain a negative electrode plate.
  • the coating weights of the first slurry and second slurry were the same.
  • a surface density of the negative electrode film layer on one side was 12.5 mg/cm 2
  • a compacted density of the negative electrode film layer on one side was 1.80 g/cm 3 .
  • NCM811 LiNi 0.8 Co 0.1 Mn 0.1 O 2
  • a conductive agent Super P a conductive agent
  • a binder polyvinylidene fluoride a binder polyvinylidene fluoride
  • NMP solvent an appropriate amount of NMP solvent was added in the mixture, and the resulting mixture at this point was stirred into uniformity to obtain a positive electrode slurry.
  • the positive electrode slurry was applied onto two surfaces of positive electrode current collector aluminum foil, followed by drying and cold pressing, to obtain a positive electrode plate.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1:1 to obtain an organic solvent, and then LiPF 6 was dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol/L.
  • a PP/PE composite film was used as a separator.
  • the separator and the positive electrode plate and negative electrode plate prepared above were arranged in sequence so that the separator was located between the positive electrode plate and negative electrode plate to provide separation. Then the resulting stack was wound to obtain an electrode assembly.
  • the electrode assembly was placed into an outer package and dried, and the electrolyte solution was then injected. Processes such as vacuum packaging, standing, formation, and aging were performed to obtain a secondary battery. Table 1 No.
  • Second active material Second carbon-based material Second silicon-based material
  • Second active material Second carbon-based material
  • Second silicon-based material Type Carbon enveloping layer Percentage of the number of secondary particles D v 50 ( ⁇ m) Mass percentage
  • Second carbon enveloping layer Percentage of the number of secondary particles D v 50 ( ⁇ m) Mass percentage
  • Second carbon enveloping layer Percentage of the number of primary particles D v 50 ( ⁇ m) Mass percentage
  • Example 1 Artificial graphite Yes 70% 12 100% / / / / Example 2
  • Artificial graphite Yes 70% 12 100% / / / / Example 3 Artificial graphite Yes 70% 12 100% / / / / / Example 4
  • Example 6 Artificial graphite Yes 70% 12 100% / / / / / Example 7
  • the prepared secondary battery was discharged at a constant current rate of 1C to 2.8 V. Then it was charged at a charge current of 1C to 4.3 V, and continued to be charged to a current of 0.05C. At this point, the battery was in a fully charged state. After left standing the fully charged secondary battery for 5 minutes, it was discharged at constant current rates of 0.33C and 3C to 2.8 V respectively. The discharge capacities of the secondary battery at 0.33C and 3C rates were recorded. The rate performance of the secondary battery was characterized by the ratio of the discharge capacity of the secondary battery at 3C rate to the discharge capacity of the secondary battery at 0.33C rate.
  • the prepared secondary battery was charged at a constant current of 1C to 4.3 V, and then continued to be charged at this constant voltage to 0.05C.
  • the secondary battery was discharged at a constant current of 0.5C for 30 minutes to adjust the secondary battery to 50% SOC. At this point, the voltage of the secondary battery was recorded as U 1 . Then the secondary battery was discharged at 3C for 30 seconds. At this point, the voltage after discharge was recorded as U 2 , and the discharge current was recorded as I 1 .
  • the above-prepared secondary battery was charged to 4.3 V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and left standing for 5 min; and then the secondary battery was discharged the to 2.8 V at a constant current of 1C.
  • the discharge capacity at this point was recorded, and it was the discharge capacity after the first cycle.
  • the secondary battery was subjected to the charge and discharge cycling test according to the foregoing method, and a discharge capacity of each cycle was recorded.
  • Capacity retention rate (%) of the secondary battery after 300 cycles at 45°C Discharge capacity after the 300-th cycle/Discharge capacity after the first cycle ⁇ 100% Table 3 No.
  • Example 1 Discharge capacity at 3C/discharge capacity at 0.33C Direct current resistance at 25°C (m ⁇ ) Capacity retention rate after 300 cycles at 45°C
  • Example 1 82.30% 673 96.20%
  • Example 2 83.50% 661 96.50%
  • Example 3 84.10% 653 96.60%
  • Example 4 83.00% 667 96.30%
  • Example 5 78.20% 724 89.30%
  • Example 6 84.50% 615 95.10%
  • Example 7 84.20% 633 95.80%
  • Example 8 81.90% 681 96.40%
  • Example 9 81.60% 692 96.80%
  • Example 10 76.50% 771 90.50%
  • Example 11 77.20% 753 89.10%
  • Example 12 79.70% 705 89.90%
  • Example 13 81.80% 681 96.60%
  • Example 14 83.70% 651 95.70%
  • Example 15 85.10% 638 95.50%
  • Example 16 86.40% 620 95.10%
  • Example 17 75.90% 6
  • the secondary battery can achieve high energy density, and the rate performance and cycling performance of the secondary battery can be further optimized.

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